Millions of travelers are holding discounts to thousands of museums, concerts and airline rewards in their pocket without realizing it.

Credit-card companies offer hundreds of perks that most holders never use. How good are some of these perks? It depends on the card.

The great
The American Express Platinum cardholders can receive unlimited access to several airport lounges, including those run by the Delta, US Airways and American. According to MSN Money, those memberships would cost well over $1,000 if purchased individually.

Airline credit cards carry perks beyond earned miles. Some airlines, including American and Delta, allow cardholders to check their bags for free.

The pretty goodBank of America credit cards entitle users to one free general admission to select museums, including the Art Institute of Chicago and the Solomon R. Guggenheim Museum, on the first full weekend of every month. A great way to save an easy $10 or more, but not worth getting a card solely for that reason.

Many cards include a small amount of travel insurance when you purchase your trip, although it’s likely only to accentuate the travel insurance you purchase. A much better perk is the free crash insurance for rental cars that comes standard with many cards.

The so-so
Citi’s Easy Deals allows you to cash in earned points for travel perks, including slightly discounted gift cards for cruises, rental cards and hotels. The hotel and rental car deals featured on the site aren’t much better than offers you can find on Travelocity or Expedia. You can also book tickets to popular attractions, but again, the discounts are virtually nil. Tickets to the Kennedy Space Center are $50 on its website, while Citi offers the same ticket for $48 and five of your earned points.

My wife had her iPhone stolen in the Paris Metro earlier this year. Had we used a Wells Fargo credit card, we may have been eligible for $600 replacement coverage. But, of course, there are caveats. First, we would have had to pay our monthly cellular bill with the card. Also, after the phone was stolen, we would have first had to file a claim against our homeowners insurance before Wells Fargo would have paid the difference.

Before making any travel plans, check your monthly credit card bill for any potential offers, visit your bank’s website or call the toll-free number on the back of the card to find out what perks are available to you.

*This post was updated from its original version to remove reference to a credit card offered by Continental.